Changes

Permeable pavers are ideal for sites with limited space and projects such as low traffic roads, parking lots, driveways and walkways. Components include: interlocking pavers, precast pervious slabs, cast in place surface, bedding course, and underground storage layer. Additional components include an underdrain to remove excess water and soil additives to enhance pollutant removal.

Permeable pavers are ideal for sites with limited space and projects such as low traffic roads, parking lots, driveways and walkways. Components include: interlocking pavers, precast pervious slabs, cast in place surface, bedding course, and underground storage layer. Additional components include an underdrain to remove excess water and soil additives to enhance pollutant removal.

====STEP recommendations:====

==Design Assumptions==

*[[Bedding layer]] and [[Permeable pavements: Specifications|joint filler]] should consist of [[clear stone]] and [[gravel]] rather than [[sand]] to prevent [[clogging]].

Porous asphalt is ideal for sites with limited space and projects such as low traffic roads, parking lots, driveways and walkways. Components include: a porous asphalt surface, a stabilizer course, and a base layer for storage.

*Granular materials should not be applied as anti-skid agents during [[winter]] because they can quickly clog the system.

Additional components include an underdrain to remove excess water and surface drains to deal with runoff flows in excess of design capacity.

*[[Winter Management|Winter maintenance]] practices should be limited to plowing, with [[Salt|de-icing salts]] applied sparingly.

*The [[Permeable pavements: Specifications|slope]] of the permeable pavement surface should be at least 1% and no greater than 5%.

*The impervious land surrounding and draining onto the pavement should not exceed the area of the permeable pavement (1:1 / I:P ratio).

*The [[Permeable pavements: Specifications|storage layer]] must be [[Permeable pavements: Sizing|sized to accommodate runoff]] from the pavement and any impermeable areas draining to it.<br>

====Tool defaults based on STEP recommendations:====

Design and operation and maintenance program assumptions used to generate cost estimates are based on tool default values and the following STEP recommendations:

* Maximum drainage area to surface area ratio of 1:1 (or 4:1 for roofs that contribute clean runoff to the practice)

* Default Bedding depth of 50 millimeters.

*Operation and maintenance (O&M) cost estimates assume annual inspections, removal of trash and debris twice a year, and vacuum sweeping annually. Verification inspections are included every 5 years to confirm adequate maintenance, and every 15 years to confirm adequate drainage performance through in-situ surface infiltration rate testing.

* Default Base depth of 100 millimeters.

* Impervious drainage area to permeable surface area (I:P area) ratio of 1:1

* An underdrain (minimum 150 mm perforated pipe) is only needed when native soil infiltration is less than 15 mm/hr or infiltration is precluded.

* Default Stabilizing course/ Choker layer (19 mm dia. clear stone) depth of 50 millimetres.

* Default Asphalt depth of 110 millimetres.

* Default Stone resevoir (50 mm dia. clear stone) depth of 230 millimetres.

* A 150 mm diameter perforated underdrain pipe is included in Partial Infiltration and No Infiltration design configurations only.<br>

===Design Notes===

===Notes===

* The tool calculates costs for new designs and includes costs for contractor overhead and profit, material, delivery, labour, equipment (rental, operating and operator costs), hauling and disposal. Mobilization and demobilization costs not included. The tool adds 10% contingency and additional overhead.

* Operation and maintenance cost estimates include removal of sediment from the catchbasin, by annual surface vacuum sweeping, repairing of potholes and assume no rehabilitation of the porous asphalt surface is required over the 50 year timeframe.

* Design and Engineering cost estimates are not calculated by the tool and must be supplied by the user.

* The tool calculates costs for new (greenfield) development contexts and includes costs for contractor overhead and profit, material, delivery, labour, equipment (rental, operating and operator costs), hauling and disposal.  

* Unit costs are based on 2018 pricing; the tool automatically adds inflation. See the Assumptions sheet in the tool for further details.

** Land value and equipment mobilization and demobilization costs are not included, assuming BMP construction is part of overall development site construction.

* The cost of retrofitting is ~16% higher than the cost of new construction.

** Design and Engineering cost estimates are not calculated by the tool and must be supplied by the user.

** Retrofit costs are included in the 'Costs Summary' section and can be added to the Total Construction Cost for increased accuracy.<br>

<small>'''Note''': Permeable Pavements (all 3 design scenarios): Assumes that replacement of pavers occurs at 8 years, and a full rehabilitation of the practice is performed at 30 years.</small>

* Unit costs are based on 2018 RSMeans standard union pricing.

* Additional costs associated with retrofit or redevelopment contents is assumed to be 16% higher than the cost for new (greenfield) development contexts.

** Retrofit construction cost estimates are included in the 'Costs Summary' section for comparison.<br>

==Construction Costs==

==Construction Costs==